Image forming apparatus, image forming method and program

ABSTRACT

The image forming apparatus comprises a resolution converting unit configured to convert a high-resolution image data into a low-resolution image data, an edge judgment unit configured to judge a shape of an edge in the high-resolution image data, and a density correcting unit configured to make a density correction in the low-resolution image data in accordance with the shape of the edge judged by the edge judgment unit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus, an imageforming method and a program, which make a density correction forrealizing a stable reproducibility of an image in pseudo high-resolutionprocessing.

2. Description of the Related Art

In recent years, progress of a high-quality image in a printer isremarkable, and a high-resolution processing of an engine, a high speedof the processing unit accompanying the high-resolution processing andan increase in memory capacity have rapidly been progressed. However,since enormous costs are required for meeting all of them, severalmethods are at present proposed for achieving the high-quality image orthe high speed and the low costs all together.

An example of a method conventionally performed in a printer of anelectronic photo system includes a method where in a low-resolutionprinter engine, low-resolution image data are exposed on a photoconductor so as to overlap between dot pitches of each pixel (forexample, refer to Japanese Patent Laid-Open No. H04-336859(1992). Inconsequence, latent images are formed so that the overlapped portionsbetween the pixels become also effective pixels. This is called spotmultiplexing for reproducing an image with a pseudo higher resolutionthan an actual resolution.

In the above conventional technology (for example, refer to JapanesePatent Laid-Open No. H04-336859(1992), rendering is made to ahigh-resolution image data, various types of image processing areperformed to the high-resolution image data as it is, and thereafter, itis required to generate and print the low-resolution image data forprinting. Therefore, an example of a method of realizing the spotmultiplexing at low costs includes a method in which a high-resolutionimage data is converted into a low-resolution image data and thereafter,various types of image processing are performed to the low-resolutionimage data, and a pseudo high-resolution image data is reproduced usingthe spot multiplexing (for example, refer to Japanese Patent Laid-OpenNo. 2004-201283).

However, since the above spot multiplexing forms the latent image fromthe overlapping of the two adjacent exposure portions for reproducingone dot, there is a problem that the dot reproduction is unstable and isdifficult to control as compared to the usual processing. In particular,it is difficult to reproduce a small character or a thin line, which maybe reproduced in such a manner as to be blurred with a light density atbest. Therefore, the reproduction stabilization has been achieved bymaking the density correction so as to increase the density of thecharacter or the whole line, but the spot multiplexing has also an issuethat the color appearance of the character or the line largely changes.

SUMMARY OF THE INVENTION

For solving the above problems, an image forming apparatus according tothe present invention comprises a resolution converting unit configuredto convert a high-resolution image data into a low-resolution imagedata, an edge judgment unit configured to judge a shape of an edge inthe high-resolution image data, and a density correcting unit configuredto make a density correction in the low-resolution image data inaccordance with the shape of the edge judged by the edge judgment unit.

According to the present invention, since the density can be controlledlocally to the edge of the low-resolution image, the density can bestably reproduced to the edge of the low-resolution image converted fromthe high-resolution image.

Further, since only the edge is defined as an object for the densitycorrection as compared to the conventional method of making the densitycorrection in such a manner as to increase the density of the characteror the whole line, the density correction can be made to the edge whichpossibly disappears due to the resolution conversion without changingthe color appearance of the character or the whole line.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing an image forming apparatusaccording to a first embodiment;

FIG. 2 is a cross section showing the image forming apparatus accordingto the first embodiment;

FIG. 3 is a block diagram showing an image processing unit according tothe first embodiment;

FIG. 4 is a block diagram showing an edge correcting unit according tothe first embodiment;

FIG. 5 is a flowchart showing pseudo high-resolution convertingprocessing according to the first embodiment;

FIG. 6 is a diagram showing a relation between an image data forprinting and a processing rectangle according to the first embodiment;

FIG. 7 is a diagram showing a relation between a processing rectangleand a multiply accumulation calculating coefficient according to thefirst embodiment;

FIG. 8 is a diagram showing an example of a multiply accumulationcalculating coefficient according to the first embodiment;

FIG. 9 is a diagram showing an example of edge patterns according to thefirst embodiment;

FIG. 10 is a diagram showing an example of edge correction tablesaccording to the first embodiment;

FIG. 11 is a diagram showing an example of an input/outputcharacteristic in the edge correction table according to the firstembodiment;

FIG. 12 is a block diagram showing an image processing unit according toa second embodiment;

FIG. 13 is a block diagram showing an edge correcting unit according tothe second embodiment;

FIG. 14 is a diagram showing a relation between an image data forprinting and a processing rectangle according to the second embodiment;

FIG. 15 is a diagram showing a relation between a processing rectangleand a multiply accumulation calculating coefficient according to thesecond embodiment;

FIG. 16 is a diagram showing an example of a multiply accumulationcalculating coefficient according to the second embodiment;

FIG. 17 is a diagram showing an example of edge patterns according tothe second embodiment;

FIG. 18 is a diagram showing an example of edge correction tablesaccording to the second embodiment;

FIG. 19 is a diagram showing an example of an input/outputcharacteristic in the edge correction table according to the secondembodiment;

FIG. 20 is a diagram showing an example of edge correction tablesaccording to a third embodiment;

FIG. 21 is a diagram showing an example of an input/outputcharacteristic in the edge correction table according to the thirdembodiment;

FIG. 22 is a diagram showing an example of edge tables according to thethird embodiment;

FIG. 23 is a diagram showing an example of an image data for printingaccording to the first embodiment; and

FIG. 24A is an example showing the result of pseudo high-resolutionconverting processing according to the first embodiment.

FIG. 24B is an example showing the result of pseudo high-resolutionconverting processing according to the first embodiment.

FIG. 24C is an example showing the result of pseudo high-resolutionconverting processing according to the first embodiment.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, best modes for carrying out the present invention will beexplained with reference to the accompanying drawings.

First Embodiment

FIG. 1 is a schematic block diagram showing an image forming apparatus,and a block diagram showing a digital complex machine having generalfunctions of copying, printing, faxing, and so on.

An image forming apparatus 10 in a first embodiment shown in FIG. 1includes a scanner unit 101 for performing manuscript reading processingand a controller 102.

Here, an image processing unit 301 for performing image processing to animage data read from the scanner unit 101 and a memory 105 for storingdata are stored in the controller 102.

The image forming apparatus 10 further includes an operation unit 104for setting various printing conditions to the image data read from thescanner unit 101.

The image forming apparatus 10 includes a printing unit 103 forperforming image formation of visualizing the image data read from thememory 105 on a print sheet according to a print setting condition setby the operation unit 104.

The image forming apparatus 10 is connected through a network 106 to aserver 107 for managing the image data and a personal computer (PC) 108for instructing execution of printing to the image forming apparatus 10.

Here, apparatuses other than the image forming apparatus 10, the server107 and the PC 108 may be connected to the network 106.

In FIG. 1, the scanner unit 101, the printing unit 103, the operationunit 104 and the network 106 are connected to the controller 102.

FIG. 2 is a cross section showing the image forming apparatus 10. Byreferring to FIG. 2, the image forming apparatus 10 in FIG. 1 will be inmore detail explained.

The image forming apparatus 10 has the functions of copying, printingand faxing. As shown in FIG. 2, the image forming apparatus 10 in thefirst embodiment includes the scanner unit 101, a document feeding (DF)unit 202 and the printing unit 103.

First, a reading operation of an image performed mainly by the scannerunit 101 will be explained. In a case of setting a manuscript on amanuscript table 207 in FIG. 2 to read the manuscript, the manuscript isset on the manuscript table 207 and the DF 202 is closed. Thereafter, anopening/closing sensor 224 detects that the manuscript table 207 hasbeen closed, and optical reflection type manuscript-size detectingsensors 226 to 230 accommodated in a casing of the scanner unit 101detect a size of the manuscript set on the manuscript table 207. A lightsource 210 starts to illuminate the manuscript based upon the sizedetection and a CCD (charge-coupled device) 231 receives reflected lightthrough a reflecting plate 211 and a lens 212 from the manuscript toread an image. The controller 102 in the image forming apparatus 10converts the image data read by the CCD 231 into a digital signal,performing image processing for scanning, and stores the image as imagedata for printing in the memory 105 in the controller 102.

In a case of setting a manuscript on the DF 202 to read the manuscript,the manuscript is so arranged as to face up on a tray of a manuscriptsetting unit 203 in the DF 202. Thereafter, a manuscript detectingsensor 204 detects that the manuscript is set, and a sheet feedingroller 205 and a carrier belt 206 rotate in response to this detectionto carry the manuscript, which is thereafter set at a predeterminedposition on the manuscript table 207. Subsequently, the image data isread in the same way as in a case where the image is read on themanuscript table 207 and the obtained image data for printing is storedin the memory 105 in the controller 102.

Completion of the image reading causes the carrier belt 206 to rotateonce more and feed the manuscript to a right side in the cross sectionof the image forming apparatus in FIG. 2, and the manuscript isdischarged to a manuscript discharging tray 209 via a carrier roller 208in the discharged side. In a case where a plurality of manuscriptsexist, the manuscript is discharged and carried to the right side in thecross section of the image forming apparatus from the manuscript table207 and at the same time, the next manuscript is fed from the left sidein the cross section of the image forming apparatus via the sheetfeeding roller 205, thus continuously performing the reading of the nextmanuscript. The operation of the scanner unit 101 is performed asdescribed above.

Next, a printing operation performed mainly at the printing unit 103will be explained. The image data for printing once stored in the memory105 in the controller 102 is once more subject to image processing forprinting, which will be described later, in the controller 102 andthereafter, is transferred to the printing unit 103. In the printingunit 103, the image data is converted into a pulse signal by PWM controlin the printing unit 103 and at a laser printing unit, is converted intoprint laser light of four colors composed of yellow, magenta, cyan, andblack. The print laser light illuminates a photosensitive element 214 ofeach color to form an electrostatic latent image on each photosensitiveelement 214. The printing unit 103 performs a toner phenomenon to eachphotosensitive element by toner supplied from a toner cartridge 215 anda toner image visualized on each photosensitive element is primarilytransferred on an intermediate transfer belt 219. The intermediatetransfer belt 219 rotates in a clockwise orientation in FIG. 2. When aprint paper fed from a sheet cassette 216 through a sheet feedingcarrier path 217 arrives at a secondary transfer position 218, the tonerimage is transferred from the intermediate transfer belt 219 onto theprint paper.

At a fixing container 220, toner is fixed by pressurizing and heating onthe print paper on which the image is transferred, and the print paperis carried to the sheet delivery carrier path. Thereafter, the printpaper is discharged to a center tray 221 at a face downward or a sidetray 222 at a face upward. A flapper 223 changes the carrier path forchanging these sheet discharging openings. In a case of double-facedprinting, after the print paper passes through the fixing container 220,the flapper 223 changes the carrier path and thereafter, the print paperis switched back in a downward orientation, and the print paper is fedthrough a paper carrier path 225 for double-faced printing at thesecondary transfer position 218 once more, thus performing thedouble-faced printing.

Next, the aforementioned image processing for printing will be explainedwith reference to FIG. 3.

FIG. 3 is a block diagram showing the image processing unit 301.

The image processing unit 301 in FIG. 3 performs image processing forprinting in the controller 102 in FIG. 1. Here, the image data forprinting once printed in the memory 105 in the controller 102 is data ofeight bits and has the color number of 256 gradations per one pixel.Pseudo high-resolution converting processing to be described later isperformed to the image data for printing input from the memory 105 at apseudo high-resolution converting processing unit 302, therebyconverting the image data with a resolution of 1200 dpi into that withresolution of 600 dpi. Thereafter, a gamma correction is made in a gammacorrecting unit 303, and in the half tone processing unit 304, the imagedata for printing of eight bits is converted into that of four bitsprintable in the printing unit 103, which is thereafter delivered to theprinting unit 103.

A CPU 306 in FIG. 3 controls an operation of the entire image processingunit 301 based upon a control program stored in a ROM 305. A RAM 307 isused as an operational region of the CPU 306. In the RAM 307, besides, amultiply accumulation calculating coefficient to be described later,edge patterns for edge judgment and edge correction tables used for adensity correction of the edge are recorded.

Next, the processing of the pseudo high-resolution converting processingunit 302 in FIG. 3 will be in detail explained with reference to FIGS. 3to 6.

FIG. 4 is a block diagram showing an edge correcting unit 310 in FIG. 3.FIG. 5 is a flow chart showing the pseudo high-resolution convertingprocessing in the pseudo high-resolution converting processing unit 302in FIG. 3. FIG. 6 is a diagram showing a relation between an image datafor printing and a processing rectangle in the pseudo high-resolutionconverting processing.

First, at step S501 in FIG. 5, a multiply accumulation calculatingprocessing unit 309 in FIG. 3 performs the multiply accumulationcalculating processing to be described later. A processing rectanglehaving nine pixels with a sum of a width of 3 pixels and a height of 3pixels used in the multiply accumulation calculating processing is inputfrom the image data for printing of 1200 dpi corresponding to threelines delayed by two lines at a FIFO memory 308 to the multiplyaccumulation calculating processing unit 309. The image data forprinting of 600 dpi is outputted by one pixel from the multiplyaccumulation calculating processing unit 309 by the multiplyaccumulation calculating processing.

FIG. 6 shows a relation between an image data 601 for printing of 1200dpi and a processing rectangle 604 composed of nine pixels around apixel of interest 603. Since the pseudo high-resolution convertingprocessing in the present embodiment is the converting processing from1200 dpi into 600 dpi, the processing rectangle 604 is sequentiallygenerated to the image data 601 for printing of 1200 dpi in such amanner that the pixel of interest 603 corresponds to positions 602 whichare spaced by an interval of one pixel longitudinally or laterally.

Next, at step S502 in FIG. 5, a binarization processing unit 401 in theedge correcting unit 310 shown in FIG. 4 processes the processingrectangle 604 of 1200 dpi to be binary. The binarization processingconverts all values of the nine pixels in the processing rectangle 604in FIG. 6 into numeral 1 (black pixel) when the value is larger than abinarization threshold value and into numeral 0 (white pixel) when thevalue is equal to or smaller than the binarization threshold value. Inthe present embodiment, the binarization threshold value is made tonumeral 0 as one example.

Next, at step S503 in FIG. 5, the edge judgment unit 402 in the edgecorrecting unit 310 shown in FIG. 4 performs edge judgment processing tobe described later. The edge judgment unit 402 judges whether or not theresult of the binarization of the rectangle region 604 binarized by thebinarization processing at step S502 corresponds to an edge pattern tobe described later.

Next, in a case where the edge judgment processing at step S503 judgesthat the edge pattern corresponding to the binarization result exists,at step S504 it is judged that the processing rectangle 604 in FIG. 6 isan edge, and the process goes to step S505. In a case where the edgejudgment processing at step S503 judges that the edge patterncorresponding to the binarization result does not exist, at step S504 itis judged that the processing rectangle 604 is not the edge, and onepixel of 600 dpi found at step S501 is outputted without performingdensity correcting processing to be described later.

Next, at step S505, the edge judgment unit 402 in the edge correctingunit 310 shown in FIG. 4 outputs an edge number corresponding to theedge pattern in accordance with the binarization result of theprocessing rectangle 604 in FIG. 6. The density correcting unit 403 inthe edge correcting unit 310 shown in FIG. 4 determines an edgecorrection table used for the density correcting processing from theoutputted edge number.

Finally, at step S506, the density correcting unit 403 in the edgecorrecting unit 310 performs the density correcting processing to theone pixel of 600 dpi found at step S501 by using the edge correctiontable determined at step S505, and thereafter, outputs the image data. Adetail of the density correcting processing and the edge correctiontable will be explained later.

Next, by referring to FIGS. 6 to 8, a detail of the multiplyaccumulation calculating processing performed at the multiplyaccumulation calculating processing unit 309 of FIG. 3 will beexplained.

FIG. 7 is a diagram showing a relation between a processing rectangleand a multiply accumulation calculating coefficient in the multiplyaccumulation calculating processing. As described above, the processingrectangle 604 in FIG. 6 input to the multiply accumulation calculatingprocessing unit 309 in FIG. 3 is constructed of a sum of nine pixelsaround the pixel of interest 603. The multiply accumulation calculatingcoefficient 701 in FIG. 7 has nine values a to i corresponding to therespective nine pixels contained in the processing rectangle 604. Whencoordinates of the pixel of interest 603 in FIG. 7 are made of (j, i)and a value of a pixel is I (j, i), the result OUT of the multiplyaccumulation calculating processing is found according to the followingformula.

OUT=(I(j−1, i−1)×a+I(j−1, i)×b+I(j−1, i+1)×c+I(j, i−1)×d+I(j, i)×e+I(j,i+1)×f+I(j+1, i−1)×g+I(j+1, i)×h+I(j+1, i+1)×i)>>6

In this calculation, a product of each pixel in the processing rectangle604 in FIG. 7 and a value of the multiply accumulation calculatingcoefficient 701 corresponding to the coordinates of the pixel is found,and the products corresponding to nine pixels are summed up, which areshifted right by six bits. This bit shift means that the summed value ofthe nine pixels is divided by 64. A sum of a to i of the multiplyaccumulation calculating coefficient 701 in FIG. 7 is set so as to be64. A multiply accumulation calculating coefficient 801 in FIG. 8 is anexample in regard to values a to i of the multiply accumulationcalculating coefficient 701 in the present embodiment, and a sum of themultiply accumulation calculating coefficient 801 is 64 as describedabove.

Here, in the above multiply accumulation calculating processing, a sumof the products is divided by 64, but not limited thereto and forexample, a sum of the products by the processing rectangle 604 may bedivided by a sum of a to i of the multiply accumulation calculatingcoefficient 701 in FIG. 7. a to i of the multiply accumulationcalculating coefficient 701 in FIG. 7 are made to a decimal figure, andthe sum is made to one. In consequence, it is required only to find asum of the products by the processing rectangle 604.

Next, by referring to FIGS. 9 to 11, a detail of the edge judgmentprocessing performed at the edge judgment unit 402 in the edgecorrecting unit 310 shown in FIG. 4, the edge patterns used in the edgejudgment processing, and the edge correction tables used in the densitycorrecting unit 403 will be explained.

FIG. 9 is an example showing edge patterns in the present embodiment.FIG. 10 is an example showing edge correction tables associated with theedge patterns according to the present embodiment. FIG. 11 is a diagramshowing an input/output characteristic in the edge correction table witha graph of two axes.

An edge pattern 901 in FIG. 9 is a pattern called the edge number of 0in which only one pixel of nine pixels in the upper right corner hasnumeral 1 and each pixel other than that has numeral 0. The edge pattern901 in FIG. 9 is made associated with an edge correction table 1001 inFIG. 10 and is stored in the RAM 307 in FIG. 3. Likewise, an edgepattern 902 in FIG. 9 called the edge number of 1 is made associatedwith an edge correction table 1002 in FIG. 10 and is stored in the RAM307 in FIG. 3. An edge pattern 903 in FIG. 9 called the edge number of 2is made associated with an edge correction table 1003 in FIG. 10 and isstored in the RAM 307 in FIG. 3. Likewise, in the present embodiment,the edge patterns 901 to 916 corresponding to the edge numbers 0 to 15in FIG. 9 and the edge correction tables 1001 to 1016 in FIG. 10 aremade associated with each other and are stored in the RAM 307 in FIG. 3.

In the edge judgment processing at step S503 in FIG. 5, the processingrectangle 604 which is binarized to numeral 1 or 0 by the binarizationprocessing unit 401 in FIG. 4 and all of the edge patterns 901 to 916 inFIG. 9 are compared. It is judged whether or not each of the edgepatterns 901 to 916 in FIG. 9 corresponds to the binarized processingrectangle 604. When any of the edge patterns corresponding to theprocessing rectangle exists, the edge number of the corresponding edgepattern is outputted to the density correcting unit 403 in FIG. 4.

FIG. 11 is a graph showing input/output characteristics in the edgecorrection tables 1001 to 1016 in FIG. 10.

The input/output characteristic in the edge correction table 1001 inFIG. 10 is shown in a graph 1101 in FIG. 11. The input/outputcharacteristic in the edge correction table 1002 in FIG. 10 is shown ina graph 1102 in FIG. 11. The input/output characteristic in the edgecorrection table 1003 in FIG. 10 is shown in a graph 1103 in FIG. 11.The input/output characteristic in the edge correction table 1004 inFIG. 10 is shown in a graph 1104 in FIG. 11.

For example, in the graph 1101 in FIG. 11 showing the input/outputcharacteristic of the edge correction table 1001 in FIG. 10, an outputvalue minus an input value is larger than in any of the graphs 1102 to1104 showing the other input/output characteristics. Since this relationallows one pixel of 600 dpi to which the edge correction table 1001 inFIG. 10 is applied to largely increase the value in the densitycorrecting processing performed at the density correcting unit 403 inFIG. 4, the edge density is strongly corrected, thus enabling the stabledensity reproduction.

On the other hand, in the graph 1104 in FIG. 11 showing the input/outputcharacteristic in the edge correction table 1004 in FIG. 10 madeassociated with the edge pattern 904 in FIG. 9, the input value isnearly equal to the output value. Therefore, it can be said that thedensity correction is not made in the density correcting unit 403 inFIG. 4.

In the graphs 1102 and 1103 in FIG. 11 showing the input/outputcharacteristics in the edge correction tables 1002 and 1003 in FIG. 10made associated with the edge patterns 902 and 903 in FIG. 9, anintermediate density correction between the two edge correction tablesis made. That is, in the edge pattern in which the numbers of numeral 1are small (the numbers of black pixel are small), the pixel is convertedinto one pixel of 600 dpi having a very thin density by the multiplyaccumulation calculating processing to make the density reproductionunstable, therefore correcting the edge density strongly. In reverse, inthe edge pattern in which the numbers of numeral 1 are the larger (thenumbers of black pixel are larger), the pixel is converted into onepixel of 600 dpi having the stronger density by the multiplyaccumulation calculating processing, therefore correcting the edgedensity lightly.

In the edge correction tables 1001 to 1016 in FIG. 10, the densitycorrection is made in consideration of characteristics of orientation inthe edge patterns 901 to 916 in FIG. 9.

Since numeral 1 concentrates on the right side in the edge patterns 901to 904 in FIG. 9, the edge patterns 901 to 904 form a pattern group fordetecting edges in a specific orientation mainly at the left side.

Likewise, the edge patterns 905 to 908 of FIG. 9 form a pattern groupfor detecting edges in a specific orientation mainly at the lower side,the edge patterns 909 to 912 form a pattern group for detecting edges ina specific orientation mainly at the right side, and the edge patterns913 to 916 form a pattern group for detecting edges in a specificorientation mainly at the upper side.

In FIG. 10, the edge correction tables 1013 to 1016 in the pattern groupfor detecting the edges at the upper side controls the densitycorrection in accordance with the numbers of numeral 1 (the numbers ofblack pixel) in the same way as the edge correction tables 1001 to 1004in the pattern group for detecting the edges at the left side.

On the other hand, the edge correction tables 1005 to 1012 in FIG. 10 inthe pattern group in the edge patterns 905 to 912 in FIG. 9 fordetecting the edges in the other orientation do not make the densitycorrection in accordance with the numbers of numeral 1 (the numbers ofblack pixel) in the edge pattern, as understood from the graphs 1105 to1112 in FIG. 11 showing the input/output characteristics.

Making the density correction substantially equally in the edges in allorientations including every specific orientation allows stable densityreproduction and in reverse, prevents a color appearance of a thin lineor a thin character from largely changing after printing or a thin lineor a thin character from becoming a thick line or a thick characterafter printing.

FIG. 23 is a diagram showing an example of an image data 601 forprinting of 1200 dpi. A line having a width of three pixels is drawn ina center of the image data for printing 601 in FIG. 23.

FIGS. 24A, 24B and 24C are examples showing the result of a pseudohigh-resolution converting processing to the image data for printing inFIG. 23. FIG. 24A shows an image data of 600 dpi immediately after themultiply accumulation calculating processing is performed. FIG. 24Bshows an image data of 600 dpi after the edge correcting processing isperformed using the edge pattern and the edge correction table in thepresent embodiment. FIG. 24C is an image data of 600 dpi in a case wherethe density correction is made equally in strength to the edges in allorientations not considering the characteristic of orientation of theedge. It is to be understood that in FIG. 24C, thick lines arereproduced as each having a thicker density than in FIG. 24A or FIG.24B.

It should be noted that in the explanation of the present embodiment,the density correction is made only to the edges at the upper side andat the left side, but the present invention is not limited thereto, anda lighter density correction may be made to the edges, for example, atthe lower side and at the right side than at the upper side and at theleft side. Further, for example, the edges in the other orientation,such as the edges only at the lower side and at the right side may becorrected strongly in density. The edge pattern also is not limited tothe pattern described in the present embodiment.

As explained above, according to the first embodiment, the edge alone isset as an object for control, and it is possible to locally control theedge density in accordance with a shape of the edge (edge pattern).Therefore, it is possible to stabilize the spot multiplexing toreproduce the image without changing the color appearance of thecharacter or the entire line.

Second Embodiment

In the first embodiment, the pseudo high-resolution convertingprocessing by the processing rectangle having a width of three pixelsand a height of three pixels is explained in the multiply accumulationcalculating processing unit 309 and the edge correcting unit 310 in FIG.3.

In the present embodiment, pseudo high-resolution converting processingby a processing rectangle having a width of two pixels and a height oftwo pixels will be in detail explained with reference to the followingdrawings. It should be noted that since components other than the pseudohigh-resolution converting processing unit 302 are identical to those inthe first embodiment, an explanation for the components is omitted.

By referring to FIG. 5, and FIGS. 12 to 14, the processing of the pseudohigh-resolution converting processing unit 302 in FIG. 12 will be indetail explained.

FIG. 12 is a block diagram showing an image processing unit 301 in thesecond embodiment.

FIG. 13 is a block diagram showing an edge correcting unit 1203.

FIG. 14 is a diagram showing a relation between an image data forprinting and a processing rectangle in the pseudo high-resolutionconverting processing.

First, in the second embodiment, at step S501 in FIG. 5, the multiplyaccumulation calculating processing unit 1202 in FIG. 12 performsmultiply accumulation calculating processing to be described later. Theprocessing rectangle formed of four pixels with a sum of a width of twopixels and a height of two pixels in use for the multiply accumulationcalculating processing is input to the multiply accumulation calculatingprocessing unit 1202 in FIG. 12 from the image data for printing of 1200dpi corresponding to a two-line amount delayed by one-line amount at aFIFO memory 1201. According to the multiply accumulation calculatingprocessing, the image data for printing of 600 dpi is outputted by onepixel from the multiply accumulation calculating processing unit 1202.

FIG. 14 shows a relation between an image data 601 for printing of 1200dpi and a processing rectangle 1404 composed of four pixels around apixel of interest 1403. The pseudo high-resolution converting processingin the present embodiment is converting processing from the image dataof 1200 dpi into the image data of 600dpi. Therefore, the processingrectangle 1404 in FIG. 14 is sequentially generated to the image data601 for printing of 1200 dpi in such a manner that the pixel of interest1403 corresponds to positions 602 which are spaced by an interval of onepixel longitudinally or laterally.

Next, at step S502 in FIG. 5, a binarization processing unit 1301 in theedge correcting unit 1203 shown in FIG. 13 processes the processingrectangle 1404 of 1200 dpi in FIG. 14 to be binary. The binarizationprocessing converts all values of four pixels in the processingrectangle 1404 in FIG. 14 into numeral 1 when the value is larger than apredetermined binarization threshold value and into numeral 0 when thevalue is equal to or smaller than the binarization threshold value. Inthe present embodiment, the binarization threshold value is made tonumeral 0 as one example.

Next, at step S503 in FIG. 5, an edge judgment unit 1302 in the edgecorrecting unit 1203 shown in FIG. 13 performs edge judgment processingto be described later. The edge judgment unit 1302 in FIG. 13 judgeswhether or not the result of the binarization of the rectangle region1404 in FIG. 14 binarized by the binarization processing corresponds toan edge pattern to be described later.

Next, in a case where the edge judgment processing at step S503 judgesthat the edge pattern corresponding to the binarization result exists,at step S504 it is judged that the processing rectangle 1404 in FIG. 14is an edge, and the process goes to step S505.

In a case where the edge judgment processing at step S503 judges thatthe edge pattern corresponding to the binarization result does notexist, at step S504 it is judged that the processing rectangle 1404 isnot the edge, and one pixel of 600 dpi found at step S501 is outputtedwithout performing the density correcting processing to be describedlater.

Next, at step S505, the edge judgment unit 1302 in the edge correctingunit 1203 shown in FIG. 13 outputs an edge number corresponding to theedge pattern in accordance with the binarization result of theprocessing rectangle 1404 in FIG. 14. The density correcting unit 403 inthe edge correcting unit 1203 determines an edge correction table usedfor the density correcting processing from the outputted edge number.

Finally, at step S506, the density correcting unit 403 in the edgecorrecting unit 1203 in FIG. 12 performs the density correctingprocessing to the one pixel of 600 dpi found at step S501 by using theedge correction table determined at step S505, and thereafter, outputsthe image data. A detail of the density correcting processing and theedge correction table will be explained later.

Next, by referring to FIGS. 14 to 16, the multiply accumulationcalculating processing performed at the multiply accumulationcalculating processing unit 1202 in FIG. 12 will be explained.

FIG. 15 is a diagram showing a relation between a processing rectangleand a multiply accumulation calculating coefficient in the multiplyaccumulation calculating processing. As described above, the processingrectangle 1404 in FIG. 15 input to the multiply accumulation calculatingprocessing unit 1202 in FIG. 12 is constructed of a sum of four pixelsaround the pixel of interest 1403. The multiply accumulation calculatingcoefficient 1501 in FIG. 15 has four values a to d corresponding to therespective four pixels constituting the processing rectangle 1404.Coordinates of the pixel of interest 1403 in FIG. 15 are made of (j, i).When a value of a pixel is I (j, i), the result OUT of the multiplyaccumulation calculating processing is found according to the followingformula.

OUT=(I(j, i)×a+I(j, i+1)×b+I(j+1, i)×c+I(j+1, i+1)×d)>>6

In this calculation, a product of each pixel in the processing rectangle1404 in FIG. 15 and a value of the multiply accumulation calculatingcoefficient 1501 corresponding to the coordinates of the pixel is found,and the products corresponding to four pixels are summed up, which areshifted right by six bits. This hit shift means that a sum of fourpixels is divided by 64. A sum of a to d of the multiply accumulationcalculating coefficient 1501 in FIG. 15 is set so as to be 64. Amultiply accumulation calculating coefficient 1601 in FIG. 16 is anexample of values a to d of the multiply accumulation calculatingcoefficient 1501 in the present embodiment, and a sum of the multiplyaccumulation calculating coefficient 1601 is 64 as described above.

Here, in the above multiply accumulation calculating processing, a sumof the products is divided by 64, but the present invention is notlimited thereto. For example, a sum of the products by the processingrectangle 1404 may be divided by a sum of a to d of the multiplyaccumulation calculating coefficient 1501 in FIG. 15. a to d of themultiply accumulation calculating coefficient 1501 in FIG. 15 are madeto a decimal figure, and the sum is made to numeral 1. In consequence,it is required only to find a sum of the products by the processingrectangle 1404.

Next, by referring to FIGS. 17 to 19, a detail of the edge judgmentprocessing performed at the edge judgment unit 1302 of the edgecorrecting unit 1203 shown in FIG. 13, the edge pattern used in the edgecorrecting processing, and the edge correction table used in the densitycorrecting unit 403 will be explained.

FIG. 17 is an example showing edge patterns in the present embodiment.FIG. 18 is an example showing edge correction tables made associatedwith the edge patterns according to the present embodiment.

FIG. 19 is a diagram showing an input/output characteristic in the edgecorrection table with a graph of two axes.

An edge pattern 1701 in FIG. 17 is a pattern called the edge number of 0in which only one pixel in the upper right corner in four pixels hasnumeral 1 and each pixel other than that has numeral 0. The edge pattern1701 in FIG. 17 is made associated with an edge correction table 1801 inFIG. 18 and is stored in the RAM 307 in FIG. 12.

Likewise, an edge pattern 1702 in FIG. 17 called the edge number of 1 ismade associated with an edge correction table 1802 in FIG. 18 and isstored in the RAM 307 in FIG. 12. Likewise, an edge pattern 1703 calledthe edge number of 2 in FIG. 17 is made associated with an edgecorrection table 1803 in FIG. 18 and is stored in the RAM 307 in FIG.12.

In this way, in the present embodiment, the edge patterns 1701 to 1712corresponding to the edge numbers 0 to 11 in FIG. 17 and the edgecorrection tables 1801 to 1812 in FIG. 18 in FIG. 18 are made associatedwith each other and are stored in the RAM 307 in FIG. 12.

In the edge judgment processing at step S503 in FIG. 5, the processingrectangle 1404 in FIG. 14 which is binarized to numeral 1 or 0 and allof the edge patterns 1701 to 1712 in FIG. 17 are compared by thebinarization processing unit 1301 in FIG. 13. The binarizationprocessing unit 1301 in FIG. 13 judges whether or not each of the edgepatterns 1701 to 1712 in FIG. 17 corresponds to the binarized processingrectangle 1404 in FIG. 14. When any of the edge patterns correspondingto the processing rectangle exists, the edge number of the correspondingedge pattern is outputted to the density correcting unit 403.

FIG. 19 is a graph showing input/output characteristics in the edgecorrection tables 1801 to 1812 in FIG. 18.

The input/output characteristic in the edge correction table 1801 inFIG. 18 is shown in a graph 1901 in FIG. 19. The input/outputcharacteristic in the edge correction table 1802 in FIG. 18 is shown ina graph 1902 in FIG. 19. The input/output characteristic in the edgecorrection table 1803 in FIG. 18 is shown in a graph 1903 in FIG. 19.

For example, in the graph 1901 showing the input/output characteristicof the edge correction table 1801 in FIG. 18, an output value minus aninput value is larger than in each of the graphs 1902 and 1903 showingthe other input/output characteristics.

Thereby, the following effect is produced. In the same way as in thefirst embodiment, in the density correcting processing performed at thedensity correcting unit 403 in FIG. 13, one pixel of 600 dpi to whichthe edge correction table 1801 in FIG. 18 is applied results in a largeincrease in value. Therefore, one pixel of 600 dpi is strongly correctedin density, thus enabling stable density reproduction.

When the edge correction tables 1802 and 1803 in FIG. 18 made associatedwith the edge patterns 1702 and 1703 in FIG. 17 are applied to onepixel, the pixel is corrected more lightly in density than in a case ofthe edge correction table 1801. That is, in the edge pattern in whichthe numbers of numeral 1 are small, the one pixel is converted into onepixel of 600 dpi having a very thin density by the multiply accumulationcalculating processing to make the density reproduction unstable,therefore correcting the density strongly. In reverse, in the edgepattern in which the numbers of numeral 1 are the larger, one pixel isconverted into one pixel of 600 dpi having the stronger density by themultiply accumulation calculating processing, therefore correcting thedensity lightly.

In the edge correction tables 1801 to 1812 in FIG. 18, the densitycorrection is made in consideration of characteristics of orientation inthe edge patterns 1701 to 1712 in FIG. 17.

Since numeral 1 concentrates on the right side in the edge patterns 1701to 1703 in FIG. 17, the edge patterns 1701 to 1703 form a pattern groupfor detecting edges in a specific orientation mainly at the left side.

Likewise, the edge patterns 1704 to 1706 in FIG. 17 form a pattern groupfor detecting edges in a specific orientation mainly at the lower side,the edge patterns 1707 to 1709 form a pattern group for detecting edgesin a specific orientation mainly at the right side and the edge patterns1710 to 1712 form a pattern group for detecting edges in a specificorientation mainly at the upper side.

In FIG. 18, the edge correction tables 1810 to 1812 in the pattern groupfor detecting the edges at the upper side controls the densitycorrection in accordance with the numbers of numeral 1 in the same wayas the edge correction tables 1801 to 1803 in the pattern group fordetecting the edges at the left side.

On the other hand, the edge correction tables 1804 to 1809 in FIG. 18 inthe pattern group in the edge patterns 1704 to 1709 in FIG. 17 fordetecting the edges in the other orientation do not make the densitycorrection in accordance with the numbers of numeral 1 in the edgepattern as understood from the graphs 1904 to 1909 showing theinput/output characteristics.

Thereby, in the same way as in the first embodiment, making the densitycorrection substantially equal in the edges in all orientationsincluding every specific orientation prevents a color appearance of athin line or a thin character from largely changing after printing or athin line or a thin character from becoming a thick line or a thickcharacter after printing.

It should be noted that in the explanation of the present embodiment,the density correction is made only to the edges at the upper side andat the left side, but the present invention is not limited thereto, anda lighter-density correction may be made to the edges, for example, atthe lower side and at the right side than at the upper side and at theleft side. Further, for example, the edges in the other orientation,such as the edges only at the lower side and at the right side may becorrected strongly in density. The edge pattern also is not limited tothe pattern described in the present embodiment.

As explained above, according to the second embodiment, also in a casewhere the pseudo high-resolution converting processing is performed inthe processing rectangle having a height of two pixels and a width oftwo pixels, it is possible to stabilize the spot multiplexing forreproducing the image.

Third Embodiment

In the first embodiment and the second embodiment, the edge patternsused in the edge correcting unit 310 in FIG. 3 and in the edgecorrecting unit 1203 in FIG. 12 are made associated with the edgecorrection tables used in the density correcting units 403 in FIGS. 4and 13 with a relation of one to one. In addition, the edge pattern andthe edge correction table are stored at the associated state in the RAMs307 in FIGS. 3 and 12 and are used.

In the present embodiment, a method of, for cutting down on each storageregion of the RAMs 307 in FIGS. 3 and 12, associating the same edgecorrection table with a plurality of edge patterns to share the edgecorrection table will be hereinafter explained based on the firstembodiment with reference to the drawings in detail.

It should be noted that since components other than the densitycorrecting unit 403 in the present embodiment are identical to those inthe first embodiment, an explanation of the identical components isomitted.

Next, by referring to FIG. 9, and FIGS. 20 to 22, the edge judgmentprocessing performed at the edge judgment unit 402 of the edgecorrecting unit 310 shown in FIG. 4 and the density correctingprocessing performed at the density correcting unit 403 in FIG. 4 willbe explained. The edge pattern used at the edge judgment unit 402 inFIG. 4 and the edge correction table used in the density correcting unit403 will be in detail explained.

FIG. 20 is a diagram showing an example of edge correction tablesaccording to the third embodiment.

FIG. 21 is a diagram showing an example of an input/outputcharacteristic in each of edge correction tables with a graph of twoaxes.

FIG. 22 is a diagram showing an example of an edge table for associatingedge patterns with edge correction tables.

In the present embodiment, only four types of the edge correction tables2001 to 2004 in FIG. 20 to 16 types of the edge patterns 901 to 916 inFIG. 9 are stored in the RAM 307 in FIG. 3.

The respective input/output characteristics of the edge correctiontables 2001 to 2004 in FIG. 20 are shown in the graphs 2101 to 2104.

The edge patterns 901 to 916 in FIG. 9 respectively have the edgenumbers of 0 to 15. On the other hand, the edge correction tables 2001to 2004 in FIG. 20 respectively have the edge correction table numbersof 0 to 3. This respect differs from the first embodiment and the secondembodiment.

The edge patterns 901 to 916 in FIG. 9 are made associated with the edgecorrection tables 2001 to 2004 in FIG. 20 10 by an edge table 2201 inFIG. 22 stored in the RAM 307 in FIG. 3 in the same way as the edgepatterns and the edge correction tables.

The edge judgment unit 402 in FIG. 4 compares the processing rectangle604 which is binarized to numeral 1 or 0 by the binarization processingunit 401 with all of the edge patterns 901 to 916 in FIG. 9 to judgewhether or not each of the edge patterns 901 to 916 in FIG. 9corresponds to the binarized processing rectangle 604 in FIG. 6. Whenany of the edge patterns corresponding to the processing rectangleexists, the edge number of the edge pattern is outputted to the densitycorrecting unit 403 in FIG. 4.

The density correcting unit 403 in FIG. 4 obtains an edge correctiontable number from an edge table 2201 in FIG. 22 based upon an edgenumber outputted from the edge judgment unit 402. Further, the densitycorrecting unit 403 in FIG. 4 makes a density correction of the imagedata of one pixel of 600 dpi outputted from the multiply accumulationcalculating processing unit 309 in FIG. 3 using the edge correctiontable corresponding to the obtained edge correction table number.

As explained above, the third embodiment uses the edge table forassociating the edge pattern with the edge correction table. Thereby,the third embodiment can obtain the same effect as the first embodimentand the second embodiment while cutting down on a memory amount forstoring the edge density table.

Fourth Embodiment

The present invention may adopt an embodiment of a system, a apparatus,a method, a program, a memory medium or the like. Specially the presentinvention may be applied to a system constructed of a plurality of unitsor a device constructed of a single unit.

The present invention supplies a program of software realizing thefunction in the aforementioned embodiment (program corresponding to theflow chart shown in the figure in the embodiment) to the system or thedevice directly or from a remote location. Further, the presentinvention also includes a case of realizing the function of theaforementioned embodiment by reading and performing the supplied programcode by a computer equipped in the system or the device.

Accordingly, the computer program itself installed in the computer forrealizing the functional processing in the present invention with thecomputer also realizes the present invention. That is, the presentinvention includes also the computer program itself for realizing thefunctional processing in the present invention.

In this case, if equipped with the function of the program, a form suchas an object code, a program performed by an interpreter, and a scriptdata supplied to an OS may be adopted.

The print medium supplying the program includes, for example, a floppy(trade mark) disc, a hard disc, and an optical disc. Further, the printmedium includes an optical magnetic disc, a MO, a CD-ROM, a CD-R, aCD-RW, a magnetic tape, an involatile memory card, a ROM, a DVD(DVD-ROM, or DVR-R) and the like.

Besides, a supply method of the program includes connecting the programto a home page in the Internet using a browser of a client computer. Theprogram may be also supplied by downloading the computer program in thepresent invention from the home page to be connected or a file which iscompressed and includes an automatic installation function to a printmedium such as a hard disc. The supply method may be realized bydividing the program code constituting the program in the presentinvention into a plurality of tiles and downloading each file fromdifferent home pages. That is, the present invention includes also a WWWserver for downloading the program file for realizing the functionalprocessing in the present invention with a computer to a plurality ofusers.

The program in the present invention is encrypted, which is stored in amemory medium such as a CD-ROM, and the memory medium is distributed toa user. Key information for breaking the encryption is downloaded to auser meeting a predetermined condition from a home page through theInternet. The key information is used to perform the encrypted program,which is installed in the computer, realizing the function of theaforementioned embodiment.

The function in the aforementioned embodiment can be realized byperforming the program read by the computer. The function in theaforementioned embodiment can be realized by performing all or a part ofthe actual processing with an OS working on a computer based upon aninstruction of the computer program.

Further, the computer program read from the print medium is written in amemory equipped with a function expansion board inserted into thecomputer or a function expansion unit connected to the computer.Therefore, the function of the aforementioned embodiment can be realizedalso by performing all or a part of the actual processing with a CPUequipped in the function expansion board or the function expansion unitbased upon an instruction of the computer program.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2008-208597, filed Aug. 13, 2008, which is hereby incorporated byreference herein in its entirety.

1. An image forming apparatus comprising: a resolution converting unit configured to convert a high-resolution image data into a low-resolution image data; an edge judgment unit configured to judge a shape of an edge in the high-resolution image data; and a density correcting unit configured to make a density correction in the low-resolution image data in accordance with the shape of the edge judged by the edge judgment unit.
 2. An image forming apparatus according to claim 1, further comprising a binarization processing unit configured to binarize the high-resolution image data, wherein the edge judgment unit judges the shape of the edge in each rectangle region of the high-resolution image data by using the binarized image data.
 3. An image forming apparatus according to claim 2, wherein the density correcting unit changes a strength of the density correction in accordance with the numbers of black pixel contained in a rectangle region of the binarized image data.
 4. An image forming apparatus according to claim 2, wherein the density correcting unit makes the density correction more strongly as the numbers of black pixel contained in a rectangle region of the binarized image data are smaller and the density correcting unit makes the density correction more lightly as the numbers of black pixel contained in a rectangle region of the binarized image data are larger.
 5. An image forming apparatus according to claim 1, wherein the density correcting unit makes the density correction of the shape of the edge in a specific orientation.
 6. An image forming apparatus according to claim 1, wherein the density correcting unit makes the density correction using an edge correction table.
 7. An image forming apparatus according to claim 6, wherein the density correcting unit makes the density correction using an edge table for associating the edge correction table with the shape of the edge.
 8. An image forming method comprising: a resolution converting step for converting a high-resolution image data into a low-resolution image data; an edge judgment step for judging a shape of an edge in the high-resolution image data; and a density correcting step for making a density correction in the low-resolution image data in accordance with the shape of the edge judged by the edge judgment step.
 9. An image forming method according to claim 8, further comprising a binarization processing step for binarizing the high-resolution image data, wherein the edge judgment step judges the shape of the edge in each rectangle region of the high-resolution image data by using the binarized image data.
 10. An image forming method according to claim 9, wherein the density correcting step changes a strength of the density correction in accordance with the numbers of black pixel contained in a rectangle region of the binarized image data.
 11. An image forming method according to claim 9, wherein the density correcting step makes the density correction more strongly as the numbers of black pixel contained in a rectangle region of the binarized image data are smaller and the density correcting step makes the density correction more lightly as the numbers of black pixel contained in the rectangle region of the binarized image data are the larger.
 12. An image forming method according to claim 8, wherein the density correcting step makes the density correction of the shape of the edge in a specific orientation.
 13. An image forming method according to claim 8, wherein the density correcting step makes the density correction using an edge correction table.
 14. An image forming method according to claim 13, wherein the density correcting step makes the density correction using an edge table for associating the edge correction table with the shape of the edge.
 15. A computer-executable program storable in a computer readable medium for performing by a computer an image forming method comprising: a resolution converting step for converting a high-resolution image data into a low-resolution image data; an edge judgment step for judging a shape of an edge in the high-resolution image data; and a density correcting step for making a density correction in the low-resolution image data in accordance with the shape of the edge judged by the edge judgment step. 